Based on the graphic novel series “The Coldest City,” “Atomic Blonde” latches onto and never lets go of the comic book sensibility it sets up from the get-go.

Set in Berlin in November 1989 — history buffs will know that was when the Wall came down — there’s a terrific opening, with a British MI6 agent being “tagged” (spy talk for killed) by a Russian KGB agent. Fans of other brands of international espionage will be happy to learn that contingents from the American CIA and the German Stasi will also be heard from.

But first, some story development or, in more honest terminology, the beginning of much convolution. The scene shifts to London, 10 days after the Brit agent is crushed by a car in Berlin, to visit with Brit agent Lorraine Broughton (Charlize Theron), all battered and bruised, bathing in ice cubes and swilling down some vodka. After getting dressed — rather stylishly — she reports to MI6 HQ for a debriefing about the “Berlin incident.” Her superior, Eric Gray (Toby Jones), is asking the questions, while an invasive CIA man, Emmett Kurzfeld (John Goodman), is sitting by, being more of an annoyance than an official.

Lorraine, looking like she’d rather be elsewhere, starts her sordid tale, and the film shifts into flashback mode to show what she’s talking about. Here’s where I wish luck to everyone attempting to follow along. There’s something about a clandestine list of secret agents that’s fallen into the wrong hands, and how it must be recovered by the good guys. The problem: No one knows who has it. Could it be the mole-like, ever-worrying Spyglass (Eddie Marsan)? How about the nasty KGB killer Bremovych (Roland Moller)? Maybe it’s the slippery and lethal rogue operative David Percival (James McAvoy).

Lorraine, a strong, silent type, is just as slippery and dangerous as Percival, and perhaps a bit more reckless. It’s her mission to find that list, now that her partner — or was he her lover? — has been killed on the job (yeah, that run-in with the car).

Theron and McAvoy become the centerpieces here, around whom everyone else seems to revolve. For its first half, this is a slick and fast-moving film. Though she plays the part a little too cool and distant, Theron is quite good at showing off her martial arts skills. McAvoy, always fun to watch, whether you’re focusing on his constantly changing facial expressions and tics, or the many different ways he chooses to walk, remains fun to watch. There’s action to spare, involving cars and guns and knives and fists. But the film just isn’t very engaging. Maybe because the plot is too complicated, and allegiances keep changing, and you’re never really sure who’s good and who’s bad or which side anyone is actually on. One obvious mistake, which considerably slows down the pace, is the decision to have the film keep returning to the debriefing session instead of staying with the story.

Yet, there are still big kudos to go around, specifically for a brilliant piece of action choreography in one long shot with no edits (unless a few were craftily sneaked in). It begins when Lorraine and Spyglass enter a dingy apartment building, go up some steps, and become involved in fist- and gunfights galore, with villains pouring out of every doorway and corner. My guess is that it’s about a 10-minute sequence. It’s fantastic, the result of director David Leitch’s long career as a stuntman, and of his uncredited directing assistance on “John Wick.” But it comes too late to save the film from its other, less successful excesses.

The story gets so involved, so intricate, it’s impossible to understand who is the betrayer and who is being betrayed. When, at the end, everything is finally explained, it’s equally hard to tell if anything has actually been explained.

— Ed Symkus writes about movies for More Content Now. He can be reached at esymkus@rcn.com.